Detailed gravity survey indicates a Tertiary palaeochannel, 1 km wide, incised into Cambrian - Precambrian bedrock. This depression is difficult to correlate with bedrock depressions in the Port Gawler area. The palaeochannel may be of interest for underground gas storage if size, reservoir and seal conditions are suitable. A bedrock high adjacent to the coast appears to be laterally offset 5 km north of St. Kilda, which may be due to the Redbanks Fault. Follow-up survey with optical levelling and seismic control would be required to define the palaeochannel and its potential correlation with bedrock depressions further north.